[en] A new technique of 3D local structure refinement using full-potential X-ray absorption near edge structure (XANES) analysis is proposed and demonstrated in application to metalloorganic complexes of Ni. It can be applied to determine local structure in those cases where the muffin-tin approximation used in most full multiple scattering schemes fails. The method is based on the fitting of experimental XANES data using multidimensional interpolation of spectra as a function of structural parameters, recently proposed by us, and ab-initio full potential calculations of XANES using finite difference method. The small number of required ab-initio calculations is the main advantage of the approach, which allows one to use computationally time-expensive non-muffin-tin finite-difference method. The possibility to extract information on bond angles in addition to bond-lengths accessible to standard EXAFS is demonstrated and it opens new perspectives of quantitative XANES analysis as a 3D local structure probe

[en] The fine structure of X-ray emission satellite lines just below the Fermi level (Kβ satellite lines), which arise from transitions from valence bands to the core 1s level in 3d transition metals, is a developing technique and the full potential is not well known or understood. On the basis of DFT calculations for some theoretical model complexes that are relevant in bioinorganic chemistry we show that the method can be used to distinguish bonds of the metal atom with different light atoms O/N/C even if the coordination geometries are exactly the same, which is not possible using EXAFS or XANES spectroscopy. Moreover the method is sensitive to the bonding of H to the ligands, which allows to discriminate, for example, between OH- and water near the metal. Both these aspects clearly demonstrate that the Kβ satellite lines yield information that is complementary to traditional X-ray absorption spectroscopy. Good agreement between theoretical and experimental spectra for a complex Mn system was also achieved

[en] We discuss the information on the electronic structure that can be obtained by K-shell absorption and emission spectroscopy in systems that contain 3d transition metals. We remind the reader that the chemical sensitivity of the X-ray absorption near edge structure (XANES) is strongly influenced by the local geometry. The X-ray fluorescence is mostly sensitive to the electronic structure and thus complementary to XANES.

[en] A new technique for the analysis of transient X-ray absorption (also known as pump-and-probe XAS) and extraction of 3D structural information for photoexcited molecules is proposed. It is applied to metal-to-ligand-charge-transfer state of [Cu(dmp)₂]⁺ (dmp=2,9-dimethyl-1,10-phenanthroline) in acetonitrile solution. Theoretical approach combines fitting of XANES spectra with a multidimensional interpolation approximation and calculating theoretical XANES with molecular potentials beyond the muffin-tin approximation. The results of the study show that the best fit of the experimental XANES data includes a solvent molecule binding to the Cu with Cu-N distance of 2.00 A, average distance Cu-N of dmp groups is 2.04 A and that photoexcited state is characterized by significant rocking distortions of the dmp ligands.

[en] Cadmium-metallothioneins (Cd-MT) are small proteins containing seven cadmium atoms in a tetrahedral arrangement of sulfur atoms. Comparison of experimental X-ray absorption fine structure (XAFS) with theoretical full multiple-scattering XAFS spectra have been used as a tool for verification of the structural models generated using both available experimental NMR data and theoretical simulations on the basis of molecule mechanics/molecular dynamics (MM/MD) and density functional theory (DFT)

[en] Three alternative approaches have been applied to calculate As K-edge XANES of InAs: multiple scattering (MS) theory, non-muffin-tin finite difference method (FDM) and full potential linearized augmented plane wave (FLAPW) method. Such combination allows to make the distinction between two types of non-muffin-tin effects. First, in the interstitial region the potential is not constant. Second, the covalent bonds increase the charge density between nearest atoms and lead to additional loss of spherical symmetry of the potential within MT spheres

[en] Metallothioneins are the proteins containing seven Cd atoms in tetrahedral arrangement of S atoms. For this compound full multiple scattering XAFS calculations have been used as a tool for verification of structural models generated using molecular dynamic. To determine the sensitivity of the spectrum to different structural parameters and to check does the best-fit XANES spectrum correspond to the correct structure of the complex we have tested method for Cd(SPh)₄ model compound

[en] A highly sensitive setup for measuring fluorescence-detected X-ray absorption spectroscopy with sub-second time resolution has been developed at the SuperXAS beamline at the Swiss Light Source. This opens new opportunities for understanding the dynamic structure of heterogeneous catalysts. A setup for fluorescence-detected X-ray absorption spectroscopy (XAS) with sub-second time resolution has been developed. This technique allows chemical speciation of low-concentrated materials embedded in highly absorbing matrices, which cannot be studied using transmission XAS. Using this setup, the reactivity of 1.5 wt% Pt/CeO₂ catalyst was studied with 100 ms resolution during periodic cycling in CO- and oxygen-containing atmospheres in a plug-flow reactor. Measurements were performed at the Pt L₃- and Ce L₃-edges. The reactivity of platinum and cerium demonstrated a strong correlation. The oxidation of the catalyst starts on the ceria support helping the oxidation of platinum nanoparticles. The new time-resolved XAS setup can be applied to various systems, capable of reproducible cycling between different states triggered by gas atmosphere, light, temperature, etc. It opens up new perspectives for mechanistic studies on automotive catalysts, selective oxidation catalysts and photocatalysts.

[en] Ni-isocyanide and Ni-acac complexes have been studied by X-ray absorption spectroscopy. Theoretical analysis has been done using self-consistent full multiple scattering (MS) approach within both muffin-tin (MT) model of the potential and non-MT finite deference method. For the isocyanide complex, it was shown that MS theoretical spectra reproduce all structural details of the X-ray absorption near-edge structure (XANES), but also that it is important to consider the non-MT effects in the potential for a correct simulation of the shape of the pre-edge structures. The contribution of a non-constant potential in the interstitial regions is extremely important for the interpretation of the XANES of Ni(acac)₂

[en] Different AlN nanosystems (NP) were investigated by using synchrotron radiation spectroscopy. Experiments were performed at the Synchrotron Radiation Facility of the Laboratori Nazionali di Frascati using X-ray absorption near-edge spectroscopy (XANES). Preliminary XANES theoretical analysis at the Al K edge is presented